1. Field of the Invention
The present invention relates to the field of networks. More particularly, embodiments of the invention relate to a method, circuit, and system for performing integrated adjustable short-haul/long-haul time domain reflectometry.
2. Description of the Related Art
In network environments, network cabling is a common source of problems. Often, cable test equipment is used by a technician to certify that a cable within the network is working properly. A wide array of cable test equipment is available to diagnose problems associated with cables in a network.
One particular type of cable test equipment often used by a technician is a time domain reflectometer, which can implement time domain reflectometery (TDR) functionality. TDR equipment is used to locate breaks or opens in cables. TDR equipment accomplishes this by sending a pulse through a cable and by measuring the time it takes for the pulse to reflect back to the TDR equipment. Reflections occur at opens in the cable. Thus, if there is an open somewhere down the cable, the pulse that was sent out will be reflected on the open and the reflection of the pulse returns to the TDR equipment. If no reflection returns, this is an indication that there is not an open on the cable (or that the open is so far down the cable that the reflection on the cable is not detectable).
Typically, TDR equipment transmits a pulse of a predetermined width and amplitude down the cable. If the reflection comes back, the elapsed time between the time at which the TDR pulse is completely transmitted from the TDR equipment and the time at which the reflection comes back, serves as an indication of how far from the TDR equipment the open is. The TDR equipment can take this elapsed time and convert this time to distance such that a distance reading can be calculated measuring the distance from the TDR equipment to the open.
A critical parameter of the TDR functionality is the width of the TDR pulse that is being sent through the network cable. The shorter the TDR pulse sent out, the closer to the TDR equipment an open can be detected. This is because TDR equipment typically measures the time that has elapsed from the moment the TDR pulse is completely sent out to the moment its reflection returns. Therefore, the shorter the time it takes for the TDR pulse to be completely transmitted (i.e. the narrower the TDR pulse is), the sooner the TDR equipment will start timing the distance at which the open occurs. Conversely, if a really wide TDR pulse is sent out and the open is just a few feet away from the TDR equipment, the reflection will return before the TDR pulse is done transmitting, in which case the TDR equipment will ignore the reflection and the open will not be detected.
On the other hand, the wider the TDR pulse that is transmitted, the longer the reach of the TDR function (i.e. the further away an open on the cable can be detected). However, arbitrarily wide pulses cannot be used for a number of reasons. For example, most commercially available transformers on cables would saturate if the TDR pulse width is more than approximately 10 microseconds. Further, the wider the TDR pulse is that is transmitted, the longer the shortest distance is at which an open on the cable can be detected.
Moreover, wider TDR pulses can cause transformers on cables to saturate and can be followed by a slowly leaking direct current (DC) level. Thus, a voltage slope that trails the actual TDR pulse can occur that interferes with the TDR functionality. This is because the voltage slope extends past the end of the TDR pulse and can, therefore, be falsely detected by the TDR equipment as a reflection. This causes the TDR equipment to falsely detect an open very near the TDR equipment.
For example, as shown in FIG. 1, a first TDR pulse 101 is transmitted. Also, another TDR pulse 102 is transmitted at a later time. Typically, multiple TDR pulses are sent out one after another with some spacing between them. Pulse 103 is the reflection of TDR pulse 101 and is coming back to the TDR equipment from an open on the cable down the line. As seen in FIG. 1, a trailing voltage slope 105 follows TDR pulse 101 after the end of pulse 101 and before the start of reflected pulse 103. Unfortunately, if this slope is above a certain voltage level, it can be falsely detected as a TDR reflection by the TDR equipment. Thus, the TDR equipment may falsely detect an open very close to the TDR equipment due to the trailing voltage slope 105.
Unfortunately, current TDR equipment is prone to false detections of cable opens, as previously described. Moreover, presently, when a cable within a network is suspected of not operating properly, a technician utilizing expensive TDR equipment must be sent out to the location of interest to test the cable.